There are known clock signal generation devices that generate clock signals. For instance, a clock signal is used to synchronize processing to be executed by a communication device in order to perform communication, the communication device being provided in a clock signal generation device.
The clock signal generation device generates a clock signal based on a reference signal from the outside. For instance, the reference signal is a signal in accordance with Precision Time Protocol (PTP) or a Global Positioning System (GPS) signal. Thus, communication timing may be synchronized, for instance, between communication devices each provided with a clock signal generation device. Also, for instance, the frequency of a wireless signal may be matched between communication devices each provided with a clock signal generation device.
For instance, in the case where a clock signal is generated based on a reference signal from the outside as an example of a clock signal generation device, the temperature of the clock signal generation device and frequency correction information indicating a correction amount for the frequency of the clock signal are stored in association with each other. Furthermore, the clock signal generation device, when being unable to obtain a reference signal, controls the frequency of the clock signal based on a detected temperature, and stored temperatures and frequency correction information. Thus, the clock signal generation device, even when being unable to obtain a reference signal, may achieve a clock signal frequency which is close to the frequency of a clock signal that is generated based on a reference signal.
The relationship between the temperature of the clock signal generation device and the frequency of the clock signal changes with the passage of time. After the temperature of the clock signal generation device becomes a specific temperature, a state may continue in which the temperature is different from the specific temperature. In this case, the aforementioned relationship at the time of detection of stored temperatures and frequency correction information is likely to have a large difference with the aforementioned relationship at the current time point.
Therefore, when the frequency of the clock signal is controlled based on the stored temperatures and frequency correction information, the accuracy of the frequency of the clock signal is likely to decrease as the interval between two points in time increases where the temperature of the clock signal generation device becomes the specific temperature at both points.
The following are reference documents.                [Document 1] Japanese Laid-open Patent Publication No. 2010-068065 and        [Document 2] Japanese Laid-open Patent Publication No. 2010-263503.        